By the main gallery you mean the featured, eh? Well, there's two variants.

The first one is by choosing only the needed folder, and unchecking 'featured' while submitting, look here: [link]

The second one (which was used before this new submission page and good for global moving) is moving in the gallery using the little pencil button that appears when you point your mouse on the deviation. There you can choose where to move or copy your deviations and whether you want to delete it from the current folder or not. For example your steps in 'featured' should be like this: [link] or like this: [link]

If you copy, it'll copy only the link to the deviation of course, so you won't have 10 copies of the same deviation with different comments or amount of faves, it'll be one same deviation, just visible in few folders.